wheeled grass trimmer

I'm thinking of buying one of the 2 wheeled grass trimmer, e.g. like the D.R. or the Swisher make. They are difficult to source here in Canada and pricey. Does anyone have any input about their practicality, would they be much more effective and easier on the back and arms than the hand held type. They aren't that much more expensive than the hand held. I have really heavy weeds like 3 to 4 ft. high thistles etc. and a really deep ditch with about a 45 degree slope. To me they make a lot of sense and they look very durable.
Appreciate any comments.
Ray

Wow thats some tall weeds! I would spray them and mow them over, and use a strait shaft stick trimmer w/0.95 line. I would imagine that the D.R. or the Swisher would be expensive to buy vs the hand held????